There have been numerous articles and technical papers on the dangers of operating in Low Earth Orbit (LEO) at altitudes between 160 km and 2000 km (0.03−0.3 RE) with the threat of collision with countless small and large orbital debris. This debris occupies LEO and extends out to Geostationary Earth Orbit or Geosynchronous Earth Orbit (GEO) at a circular orbit of 35,786 km (5.6 RE) above the Earth's equator. There are various inclinations and altitudes defining operational satellite orbits in proximity with a multitude of space debris. This space junk is comprised of derelict satellites, rocket bodies, and metal fragments from explosions or collisions. There are many other numerous small detectable or in many cases undetectable particles such as nuts, bolts, paint chips, gloves, etc. In one study conducted by the US Air Force, the Long Duration Exposure Facility (LDEF) was launched on board Space Shuttle Challenger in 1984. It was placed in a 477-km orbit at a 28.5° inclination and operated for 5.7 years. It contained 57 experiments. LDEF was the size of a school bus and configured as a 12-sided cylinder designed to have one long side exposed in the direction of the velocity vector at all times. LDEF was launched not only to accomplish science objectives in materials, electrical power, propulsion and electronics but to also characterize the impacts from orbital debris and natural meteoroids. In the final analysis, over 30% of the impact damage was from space debris. In total, there were over 34,000 impacts of 50 μm diameter orgreater. Tracking of the space debris is currently managed by the Air Force Joint Space Operations Center (JSpOC). The JSpOC monitors space debris greater than 10 cm in diameter and is currently tracking more than 8,500 objects. Estimates on the amount of debris less than 10 cm, range from 500,000 and up.
Space debris de-orbits over time due to increased drag forces as the orbital velocity of the debris slowly decays with increasing contact with the Earth's upper atmosphere. This takes many months or years and studies have shown that natural decay will not keep pace with the growing amount of space debris. In fact, we may be reaching a point where additional debris will result in a cascading effect of collisions generating more debris. There are numerous examples of high-speed collisions in low Earth orbit between satellites and with the space shuttle. From a NASA report (Protecting the Space Shuttle from Meteoroids and Orbital Debris) when the Space Shuttle is in a 51.6° inclination and 400 km altitude orbit, NASA's model of the debris environment predicts an average collision velocity of 9 km/s for orbital debris with a diameter of 1 cm or more.
Another study initiated via an official Inter-Agency Space Debris Coordination Committee (IADC) Action Item 27.1, Stability of the Future LEO Environment, was conducted by six IADC member agencies to investigate the projected growth of the LEO debris population. Each concluded independently that active satellite management and debris removal, including the 25-year rule, is necessary to prevent collisions in the future. As quoted from an executive summary from the IADC “ . . . Results from the six different models are consistent with one another, i.e., Even with a 90% compliance of the commonly-adopted mitigation measures, based on the ESA provided initial population of 2009, the LEO debris population is expected to increase by an average of approximately 30% in the next 200 years. Catastrophic collisions will continue to occur every 5 to 9 years. Remediation measures such as active debris removal should be considered to stabilize the future LEO environment.”
The Kessler Syndrome which helps to explain these phenomena is defined as the numerical growth of satellites and other space objects in orbit to a point where a collision with space debris will generate more debris particles which will then result in more collisions and so on until near Earth orbit becomes unusable. Many of the orbital space debris removal techniques to date have involved the use of a Satellite for delivery of a device or material and are required to operate in the same orbits as the debris. Some of these concepts include a collecting device or net for small debris, a tether or grappling device for larger objects, a laser beam targeting system, a dust injection system, or atmospheric gas injection system. Many involve high mass and energy systems that would contribute to the existing debris and become part of the problem. Some concepts have approached the problem with the intent to slow the orbital speed of the debris in such a way that it de-orbits over time but primarily rely on natural forces to eventually remove the debris over time which could take many years.
The problem will require a global plan that targets not only large debris objects but also includes smaller debris fields as well. This plan must be integrated to address all large and small debris regardless of the nation of origin and coordinated with and agreed to by all spacefaring nations. Financial support can be raised as an international tax on spacefaring nations by setting a tax rate based on the number of satellites placed in orbit by a given nation. Future satellite launches could be taxed based on the complexity of the satellite and record of prior compliance with existing debris mitigation requirements. A well-coordinated program could then be implemented in phases based on a study addressing operational interference, operational priority and/or potential risk determined by a board of international experts.